Centrifugal compressor

ABSTRACT

A centrifugal compressor includes a high-speed shaft, an impeller, a housing having a partition wall and a discharge passage, and a sealing member. The centrifugal compressor includes a bypass that is formed in the partition wall and has an inlet connected to the discharge passage and an outlet connected to a space between a back surface of the impeller and the partition wall. The inlet is located outward of the outlet and the outlet is located outward of the sealing member in a radial direction of the high-speed shaft. The bypass includes an outlet passage that extends to the outlet outwardly in the radial direction of the high-speed shaft. Air introduced from the inlet flows out of the outlet through the outlet passage so as to form a flow of air flowing away from the sealing member in the space.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2022-034327 filed on Mar. 7, 2022, the entire disclosure of which is incorporated herein by reference.

The present disclosure relates to a centrifugal compressor.

BACKGROUND ART

The centrifugal compressor includes a low-speed shaft, a high-speed shaft, an impeller, a speed-up gear, and a housing. The low-speed shaft is rotated by a drive source. The high-speed shaft rotates at a rotation speed that is higher than the rotation speed of the low-speed shaft. The impeller is mounted on the high-speed shaft. The speed-up gear transmits power of the low-speed shaft to the high-speed shaft.

The housing has an impeller chamber and a speed-up gear chamber. The impeller chamber accommodates the impeller. The speed-up gear chamber accommodates the speed-up gear and oil. The housing includes a partition wall that separates the impeller chamber from the speed-up gear chamber. The partition wall has an insertion hole through which the high-speed shaft is inserted.

The centrifugal compressor includes a sealing member disposed between the outer peripheral surface of the high-speed shaft and the inner peripheral surface of the insertion hole of the partition wall. The sealing member prevents oil, which has been supplied to the speed-up gear, from leaking from the speed-up 30 gear chamber to the impeller chamber through the insertion hole.

The housing has therein a discharge passage. Air compressed by the rotation of the impeller is discharged to the discharge passage. The air compressed by the impeller is discharged outside of the housing through the discharge passage. The air may leak to the speed-up gear chamber through the insertion hole due to an increase in the pressure in the impeller chamber with the rotation of the impeller, so that the pressure in the speed-up gear may increase. Further, for example, the oil may leak from the speed-up gear chamber to the impeller chamber through the insertion hole if the pressure in the impeller chamber is lower than the pressure in the speed-up gear, such as a case where the impeller is rotating at a low speed or a case where the operation of the centrifugal compressor has stopped.

For example, a centrifugal compressor mentioned in Japanese Patent Application Publication No. 2019-157707 includes a housing that has a pressure-relief passage for suppressing pressure increase in the speed-up gear chamber. This configuration allows release of the pressure through the pressure-relief passage even if the pressure in the speed-up gear chamber increases, thereby suppressing the pressure increase in the speed-up gear chamber. In other words, the pressure-relief passage releases the air in the speed-up gear chamber to the outside of the housing.

For example, the pressure in a space between the back surface of the impeller and the partition wall may become higher than the pressure in the speed-up gear chamber, such as a in case where the impeller keeps rotating at a high speed. If this condition persists, the temperature of the oil increases. Accordingly, the oil becomes vaporized or atomized. Furthermore, if this condition persists, the air discharged into the discharge passage may partly flow into the space between the back surface of the impeller and the partition wall. This may cause high-pressure air to leak from the space between the back surface of the impeller and the partition wall into the speed-up gear chamber through the insertion hole, thereby maintaining a state where the pressure in the speed-up gear chamber is high. The vaporized or atomized oil is discharged outside the housing through the pressure-relief passage. As a result, the amount of the oil filled in the centrifugal compressor may decrease.

The present disclosure, which has been made in light of the above-mentioned problem, is directed to providing a centrifugal compressor that is capable of suppressing a decrease in the amount of oil filled in the centrifugal compressor.

SUMMARY

In accordance with an aspect of the present disclosure, there is provided a centrifugal compressor that includes a low-speed shaft, a high-speed shaft, a speed-up gear, an impeller, a housing, and a sealing member. The low-speed shaft is rotated by a drive source. The high-speed shaft is configured to rotate at a rotation speed that is higher than a rotation speed of the low-speed shaft. The speed-up gear is configured to transmit power of the low-speed shaft to the high-speed shaft. The impeller is mounted on the high-speed shaft. The housing has an impeller chamber for accommodating the impeller, a speed-up gear chamber for accommodating the speed-up gear chamber and oil, a partition wall that separates the impeller chamber from the speed-up gear chamber and has an insertion hole through which the high-speed shaft is inserted, a pressure-relief passage for releasing air in the speed-up gear chamber to an outside of the housing, and a discharge passage to which the air compressed by rotation of the impeller is discharged. The sealing member is disposed between an outer peripheral surface of the high-speed shaft and an inner peripheral surface of the insertion hole. The centrifugal compressor includes a bypass that is formed in the partition wall and has an inlet connected to the discharge passage and an outlet connected to a space between a back surface of the impeller and the partition wall. The inlet is located outward of the outlet and the outlet is located outward of the sealing member in a radial direction of the high-speed shaft. The bypass includes an outlet passage that extends to the outlet outwardly in the radial direction of the high-speed shaft. The air introduced from the inlet flows out of the outlet through the outlet passage so as to form a flow of air flowing away from the sealing member in the space.

Other aspects and advantages of the disclosure will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure together with objects and advantages thereof, may to best be understood by reference to the following description of the embodiments together with the accompanying drawings in which:

FIG. 1 is a sectional view of a centrifugal compressor according to an embodiment of the present disclosure;

FIG. 2 is a fragmentary enlarged sectional view of the centrifugal compressor according to the embodiment; and

FIG. 3 is a sectional view of a bypass, depicting an operation of the bypass.

DETAILED DESCRIPTION OF EMBODIMENTS

The following will describe an embodiment of a centrifugal compressor with reference to accompanying FIGS. 1 and 2 . The centrifugal compressor of the present embodiment is mounted on a fuel cell vehicle including a fuel cell as a power source, and is configured to supply air to the fuel cell.

<Configuration of Centrifugal Compressor>

As illustrated in FIG. 1 , a centrifugal compressor 10 includes a housing 11 having a cylindrical shape. The housing 11 includes a motor housing 12, a speed-up gear housing 13, a plate 14, and a compressor housing 15. The motor housing 12, the speed-up gear housing 13, the plate 14, and the compressor housing 15 are made of a metallic material. The motor housing 12, the speed-up gear housing 13, the plate 14, and the compressor housing 15 are, for example, made of aluminum.

The motor housing 12 includes an end wall 12 a having a plate-like shape and a peripheral wall 12 b having a cylindrical shape. The peripheral wall 12 b protrudes from an outer peripheral portion of the end wall 12 a. The speed-up gear housing 13 includes an end wall 13 a having a plate-like shape and a peripheral wall 13 b having a cylindrical shape. The peripheral wall 13 b protrudes from an outer to peripheral portion of the end wall 13 a.

An end of the peripheral wall 12 b of the motor housing 12 that is distant from the end wall 12 a is connected to the end wall 13 a of the speed-up gear housing 13. An opening of the peripheral wall 12 b of the motor housing 12 is closed by the end wall 13 a of the speed-up gear housing 13. The speed-up gear housing 13 has a through hole 13 h formed through the center portion of the end wall 13 a.

The plate 14 is disposed at an end of the peripheral wall 13 b of the speed-up gear housing 13 that is distant from the end wall 13 a. The plate 14 has an insertion hole 14 h formed through the center portion of the plate 14. The plate 14 includes a first plate 141 and a second plate 142. The first plate 141 has a plate-like shape. The first plate 141 has opposite surfaces, i.e., a first surface 141 a and a second surface 141 b. The first surface 141 a is in contact with the end of the peripheral wall 13 b of the speed-up gear housing 13 that is distant from the end wall 13 a. The first plate 141 has an accommodation recess 143 that is recessed from the second surface 141 b in the thickness direction of the first plate 141. The first plate 141 has a first insertion hole H1 that is formed through the first plate 141 in the thickness direction. The first insertion hole H1 opens to the bottom portion of the accommodation recess 143.

The second plate 142 has a plate-like and ring shape. The second plate 142 is disposed in the accommodation recess 143, and the thickness direction of the second plate 142 corresponds to the thickness direction of the first plate 141. The second plate 142 is placed on the bottom of the accommodation recess 143. The second plate 142 has a second insertion hole H2. The second insertion hole H2 is communicated with the first insertion hole H1. The insertion hole 14 h of the plate 14 is formed of the first insertion hole H1 and the second insertion hole H2. The second plate 142 is fixed to the first plate 141 by a fastener (not illustrated), such as a bolt or the like, with the second plate 142 contacting the bottom of the accommodation recess 143.

The end of the peripheral wall 13 b of the speed-up gear housing 13 that is distant from the end wall 13 a is connected to the first plate 141. An opening of the peripheral wall 13 b of the speed-up gear housing 13 is closed by the plate 14.

The compressor housing 15 is connected to the second surface 141 b of the first plate 141. The motor housing 12, the speed-up gear housing 13, the plate 14, and the compressor housing 15 are arranged in this order in the axial direction of the housing 11, for example.

The compressor housing 15 has a suction passage 15 a through which air is introduced. The suction passage 15 a is opened on a center portion of an end face of the compressor housing 15 that is distant from the plate 14. The suction passage 15 a extends, in the axial direction of the housing 11, from the center portion of the end face of the compressor housing 15 that is distant from the plate 14.

<Low-Speed Shaft and Electric Motor>

The centrifugal compressor 10 includes a low-speed shaft 16 and an electric motor 17. The electric motor 17 is configured to rotate the low-speed shaft 16. That is, the low-speed shaft 16 is rotated by the electric motor 17. The electric motor 17 is a drive source configured to rotate the low-speed shaft 16.

The housing 11 has a motor chamber 25 for accommodating the electric motor 17. The motor chamber 25 is defined by the inner surface of the end wall 12 a and the inner peripheral surface of the peripheral wall 12 b of the motor housing 12 and the outer surface of the end wall 13 a of the speed-up gear housing 13. The axial direction of the low-speed shaft 16 accommodated in the motor housing 12 corresponds to the axial direction of the axis of the motor housing 12. The low-speed shaft 16 is made of a metallic material, such as iron or alloy, for example.

The motor housing 12 includes a boss 12 f having a cylindrical shape and projecting from the inner surface of the end wall 12 a. One end of the low-speed shaft 16 is inserted in the boss 12 f. A first bearing 18 is disposed between the one end of the low-speed shaft 16 and the boss 12 f. The one end of the low-speed shaft 16 is rotatably supported by the end wall 12 a of the motor housing 12 via the first bearing 18.

The other end of the low-speed shaft 16 is inserted through the through hole 13 h. A second bearing 19 is disposed between the other end of the low-speed shaft 16 and the through hole 13 h. The other end of the low-speed shaft 16 is rotatably supported by the end wall 13 a of the speed-up gear housing 13 via the second bearing 19. The low-speed shaft 16 is rotatably supported by the housing 11. The other end of the low-speed shaft 16 protrudes into the speed-up gear housing 13 through the motor chamber 25 and the through hole 13 h.

A sealing member 20 is disposed between the other end of the low-speed shaft 16 and the through hole 13 h. The sealing member 20 seals a gap between the outer peripheral surface of the low-speed shaft 16 and the inner peripheral surface of the through hole 13 h.

The electric motor 17 includes a stator 21 having a cylindrical shape and a rotor 22 disposed inside the stator 21. The rotor 22 is fixed to the low-speed shaft 16. The rotor 22 rotates together with the low-speed shaft 16. The rotor 22 includes a rotor core 22 a having a cylindrical shape and fixed to the low-speed shaft 16 and a plurality of permanent magnets (not illustrated) disposed in the rotor core 22 a.

The stator 21 surrounds the rotor 22. The stator 21 includes a stator core 21 a having a cylindrical shape, and a coil 21 b. The stator core 21 a is fixed to the inner peripheral surface of the peripheral wall 12 b of the motor housing 12. The coil 21 b is wrapped around the stator core 21 a. The coil 21 b receives current, so that the rotor 22 is rotated together with the low-speed shaft 16.

<Speed-Up Gear, High-Speed Shaft, and Speed-Up Gear Chamber>

The centrifugal compressor 10 further includes a speed-up gear 30 and a high-speed shaft 31. The high-speed shaft 31 is made of a metallic material, such as iron or alloy, for example. The axial direction of the high-speed shaft 31 accommodated in the speed-up gear housing 13 corresponds to the axial direction of the speed-up gear housing 13. A protruding end of the high-speed shaft 31 is distant from the motor housing 12 and protrudes into the compressor housing 15 through the insertion hole 14 h of the plate 14. That is, the high-speed shaft 31 is inserted through the insertion hole 14 h. The axis of the high-speed shaft 31 corresponds to the axis of the low-speed shaft 16.

The speed-up gear 30 is, for example, a traction drive gear (traction roller gear). The speed-up gear 30 includes a ring member 32. The ring member 32 is coupled to the other end of the low-speed shaft 16. The ring member 32 is made of metal. The ring member 32 is rotated with rotation of the low-speed shaft 16. The ring member 32 includes a base portion 33 and a cylindrical portion 34. The base portion 33 has a disc shape. The base portion 33 is coupled to the other end of the low-speed shaft 16. The base portion 33 extends toward the low-speed shaft 16 in the radial direction of the low-speed shaft 16. The cylindrical portion 34 has a cylindrical shape and extends from an outer peripheral portion of the base portion 33. The axis of the cylindrical portion 34 corresponds to the axis of the low-speed shaft 16. A part of the high-speed shaft 31 is disposed inside the cylindrical portion 34.

The speed-up gear 30 includes three rollers 35. For the sake of explanation, FIG. 1 illustrates only one of the three rollers 35. The rollers 35 are disposed between the cylindrical portion 34 and the high-speed shaft 31. The rollers 35 are, for example, made of metal. The rollers 35 are made of the same metal as that of the high-speed shaft 31, such as iron or iron alloy, for example. The rollers 35 are spaced from each other by a predetermined distance in the circumferential direction of the high-speed shaft 31. For example, the rollers 35 are spaced 120 degrees from each other in the circumferential direction of the high-speed shaft 31. The rollers 35 have the same shape. The rollers 35 come in contact with both of the inner peripheral surface of the cylindrical portion 34 and the outer peripheral surface of the high-speed shaft 31.

The speed-up gear 30 includes a support member 37. The support member 37 cooperates with the plate 14 to support the rollers 35 such that the rollers 35 are rotatable. The support member 37 has a bolt insertion hole 39 through which a bolt 38 is inserted. The support member 37 is fixed to the plate 14 by the bolt 38 that is screwed into the plate 14 through the bolt insertion hole 39. The rollers 35 are rotatably supported by the support member 37 and the plate 14 via a roller bearing 36.

The rollers 35, the ring member 32, and the high-speed shaft 31 are unitized with the rollers 35 pressed against the high-speed shaft 31 and the cylindrical portion 34. The high-speed shaft 31 is rotatably supported by the rollers 35. The low-speed shaft 16 and the ring member 32 are rotated by the electric motor 17 driven, and the rotational force of the ring member 32 is transmitted to the rollers 35 to rotate the rollers 35, so that the rotational force of the rollers 35 is transmitted to the high-speed shaft 31. As a result, the high-speed shaft 31 rotates. The ring member 32 and the low-speed shaft 16 rotate at the same rotation speed, and the rollers 35 rotate at a rotation speed that is higher than the rotation speed of the low-speed shaft 16. The high-speed shaft 31 rotates at a rotation speed that is higher than the rotation speed of the rollers 35. The speed-up gear 30 causes the rotation speed of the high-speed shaft 31 to be higher than that of the low-speed shaft 16. Thus, the speed-up gear 30 transmits power of the low-speed shaft 16 to the high-speed shaft 31. Accordingly, the high-speed shaft 31 rotates at a rotation speed that is higher than the rotation speed of the low-speed shaft 16.

The housing 11 has a speed-up gear chamber 40 for accommodating the speed-up gear 30. The speed-up gear chamber 40 is defined by the inner surface of the end wall 13 a and the inner peripheral surface of the peripheral wall 13 b of the speed-up gear housing 13 and the first surface 141 a of the first plate 141. The speed-up gear chamber 40 accommodates the speed-up gear 30 and oil. The sealing member 20 prevents oil stored in the speed-up gear chamber 40 from leaking into the motor chamber 25 through the gap between the outer peripheral surface of the low-speed shaft 16 and the inner peripheral surface of the through hole 13 h.

<Impeller and Impeller Chamber>

The centrifugal compressor 10 further includes an impeller 41 having a back surface 41 a and a distal end surface 41 b. The impeller 41 has a cylindrical shape, and the diameter of the impeller 41 gradually decreases from the back surface 41 a to the distal end surface 41 b.

The housing 11 has an impeller chamber 42 for accommodating the impeller 41. The impeller chamber 42 is communicated with the suction passage 15 a. The impeller chamber 42 has an approximately cone and trapezoidal hole shape, and the diameter of the impeller chamber 42 gradually increases as the impeller chamber 42 extends away from the suction passage 15 a. The protruding end of the high-speed shaft 31 protruding into the compressor housing 15 protrudes into the impeller chamber 42. The impeller 41 is mounted on the protruding end of the high-speed shaft 31.

The impeller chamber 42 is defined by the compressor housing 15 and the plate 14. That is, the plate 14 serves as the partition wall of the present disclosure that separates the impeller chamber 42 from the speed-up gear chamber 40.

<Diffuser Passage, Discharge Chamber, and Discharge Port>

The centrifugal compressor 10 further includes a diffuser passage 43, a discharge chamber 44, and a discharge port 45. The diffuser passage 43 is defined by the plate 14 and a surface of the compressor housing 15 facing the plate 14. The diffuser passage 43 is located outward of the impeller chamber 42 in the radial direction of the high-speed shaft 31. The diffuser passage 43 is communicated with the impeller chamber 42. The diffuser passage 43 has a ring shape to surround the impeller 41 and the impeller chamber 42.

The discharge chamber 44 is located outward of the diffuser passage 43 in the radial direction of the high-speed shaft 31. The discharge chamber 44 is communicated with the diffuser passage 43. The discharge chamber 44 has a ring shape. The impeller chamber 42 is communicated with the discharge chamber 44 through the diffuser passage 43. The discharge port 45 is communicated with the discharge chamber 44. Air in the discharge chamber 44 is discharged to the discharge port 45. The discharge port 45 is connected to a fuel cell 47 via a supply passage 46.

The centrifugal compressor 10 further includes a sealing member 48. The sealing member 48 is disposed between the outer peripheral surface of the high-speed shaft 31 and the inner peripheral surface of the first insertion hole H1 of the first plate 141. Specifically, the sealing member 48 is disposed between the outer peripheral surface of the high-speed shaft 31 and the inner peripheral surface of the insertion hole 14 h of the plate 14. The sealing member 48 is, for example, a mechanical seal. The sealing member 48 prevents oil stored in the speed-up gear chamber 40 from leaking from the speed-up gear chamber 40 to the impeller chamber 42 through the insertion hole 14 h.

<Flow of Air>

Air drawn through the suction passage 15 a is introduced to the impeller chamber 42. The air introduced to the impeller chamber 42 is compressed by the impeller 41. The air compressed by the impeller 41 is discharged to the diffuser passage 43. The air discharged to the diffuser passage 43 is further compressed by the diffuser passage 43 and discharged to the discharge chamber 44. The air discharged to the discharge chamber 44 is further discharged outside the housing 11 from the discharge port 45, and supplied to the fuel cell 47 through the supply passage 46.

<Suction Passage, Discharge Passage, and Space>

The suction passage 15 a serves as a passage through which the air at a suction pressure is introduced to the impeller chamber 42. The diffuser passage 43, the discharge chamber 44, and the discharge port 45 cooperate to form a discharge passage 62 through which the air at a discharge pressure is discharged from the impeller chamber 42 flows. The discharge passage 62 serves as a passage to which the air compressed by the rotation of the impeller 41 is discharged.

As illustrated in FIG. 2 , the housing 11 has an intermediate pressure passage 63. The intermediate pressure passage 63 is a space S between the back surface 41 a of the impeller 41 and the plate 14. When the air is compressed with the rotation of the impeller 41, the pressure in the space S in the impeller chamber 42 becomes intermediate pressure that is higher than the pressure in the suction passage 15 a and lower than the pressure in the discharge passage 62.

The intermediate pressure passage 63 includes a first intermediate pressure passage 631 and a second intermediate pressure passage 632. The first intermediate pressure passage 631 is defined by the back surface 41 a of the impeller 41 and the second surface 141 b of the first plate 141. The second intermediate pressure passage 632 is defined by the back surface 41 a of the impeller 41 and the second plate 142. The first intermediate pressure passage 631 is communicated with the second intermediate pressure passage 632 in the radial direction of the high-speed shaft 31. The air, which is on the back surface 41 a of the impeller 41 in the impeller chamber 42 and has intermediate pressure higher than the pressure in the suction passage 15 a and lower than the pressure in the discharge passage 62, flows through the intermediate pressure passage 63. The intermediate pressure passage 63 is communicated with the insertion hole 14 h. As such, the suction passage 15 a, the discharge passage 62, and the intermediate pressure passage 63 are defined in the housing 11. That is, the housing 11 has the suction passage 15 a, the discharge passage 62, and the intermediate pressure passage 63.

<Configuration of Oil Circulation Passage>

As illustrated in FIG. 1 , the centrifugal compressor 10 has an oil circulation passage 70. The oil to be supplied to the speed-up gear 30 circulates through the oil circulation passage 70. The centrifugal compressor 10 includes an oil cooler 65, an oil pan 66, and an oil pump 67. The oil cooler 65 cools the oil flowing through the oil circulation passage 70. The oil cooler 65 is mounted on the peripheral wall 12 b of the motor housing 12. The oil pan 66 stores the oil flowing through the oil circulation passage 70. The oil pan 66 is formed in the outer peripheral portion of the end wall 12 a of the motor housing 12. The oil pump 67 pumps the oil out of the oil pan 66 and discharges the oil. The oil pump 67 is formed within the end wall 12 a of the motor housing 12. The oil pump 67 is, for example, a positive-displacement pump. The oil pump 67 is coupled to the one end of the low-speed shaft 16. The oil pump 67 is driven with the rotation of the low-speed shaft 16.

The oil circulation passage 70 includes a first connecting passage 71, a second connecting passage 72, a third connecting passage 73, a fourth connecting passage 74, and a fifth connecting passage 75. The first connecting passage 71 connects the speed-up gear chamber 40 to the oil cooler 65. The first connecting passage 71 extends to the inside of the peripheral wall 12 b of the motor housing 12 through the speed-up gear housing 13. One end of the first connecting passage 71 opens to the speed-up gear chamber 40. The other end of the first connecting passage 71 is connected to the oil cooler 65.

The centrifugal compressor 10 is mounted on the fuel cell vehicle such that the one end of the first connecting passage 71 opening to the speed-up gear chamber 40 is located below the speed-up gear chamber 40 in the vertical direction. Accordingly, the oil in the speed-up gear chamber 40 flows into the first connecting passage 71.

The second connecting passage 72 connects the oil cooler 65 to the oil pan 66. The second connecting passage 72 is formed in the motor housing 12. One end of the second connecting passage 72 is connected to the oil cooler 65. The other end of the second connecting passage 72 opens to the oil pan 66. The oil stored in the speed-up gear chamber 40 flows through the first connecting passage 71, the oil cooler 65, and the second connecting passage 72, and flows into the oil pan 66. While flowing through the oil cooler 65, the oil is cooled by the oil cooler 65. The oil cooled by the oil cooler 65 is stored in the oil pan 66.

The third connecting passage 73 connects the oil pan 66 to the oil pump 67. The third connecting passage 73 is formed in the motor housing 12. One end of the third connecting passage 73 opens to the oil pan 66. The other end of the third connecting passage 73 is connected to the oil pump 67.

The fourth connecting passage 74 extends through the end wall 12 a and the peripheral wall 12 b of the motor housing 12, the peripheral wall 13 b of the speed-up gear housing 13, and the first plate 141. One end of the fourth connecting passage 74 is connected to the oil pump 67. The other end of the fourth connecting passage 74 opens to the speed-up gear chamber 40.

The fifth connecting passage 75 extends through the support member 37. One end of the fifth connecting passage 75 is communicated with the fourth connecting passage 74. The other end of the fifth connecting passage 75 opens to a portion of the support member 37 facing the outer peripheral surface of the roller 35.

The oil pump 67 is driven by the rotation of the low-speed shaft 16 caused by the electric motor 17. The oil pump 67 pumps the oil out of the oil pan 66 through the third connecting passage 73, and discharges the oil to the fourth connecting passage 74. An amount of the oil discharged by the oil pump 67 increases in proportion to an increase in the rotation speed of the low-speed shaft 16. The oil discharged to the fourth connecting passage 74 is further discharged to the speed-up gear chamber 40 through the fifth connecting passage 75, and supplied to the speed-up gear 30. This provides suitable lubrication of sliding portions of the rollers 35 and the high-speed shaft 31 of the speed-up gear 30. The oil supplied to the speed-up gear 30 is stored in the speed-up gear chamber 40. Accordingly, the oil to be supplied to the speed-up gear 30 circulates through the oil circulation passage 70.

<Configuration of Pressure-Relief Passage>

The centrifugal compressor 10 further has a pressure-relief passage 76 having a first end and a second end. The first end of the pressure-relief passage 76 is communicated with the oil pan 66, and the second end of the pressure-relief passage 76 is opened on the outer surface of the end wall 12 a of the motor housing 12 to be communicated with the outside of the motor housing 12. The oil pan 66 is communicated with the speed-up gear chamber 40 through the first connecting passage 71 and the second connecting passage 72 of the oil circulation passage 70. Since the pressure-relief passage 76 is communicated with the oil pan 66, the pressure-relief passage 76 is communicated with the speed-up gear chamber 40. Accordingly, the pressure-relief passage 76 serves as a passage for releasing the air in the speed-up gear chamber 40 to the outside of the housing 11.

The second end of the pressure-relief passage 76 has a ventilation film 76 a. The ventilation film 76 a prevents foreign substances from entering the pressure-relief passage 76 from the outside. The ventilation film 76 a allows passage of gas, but does not allow passage of liquid.

<Configuration of Bypass>

As illustrated in FIG. 2 , the centrifugal compressor 10 has a bypass 144. The bypass 144 is formed in the plate 14. The bypass 144 is formed in the housing 11. The bypass 144 has an inlet 1441 and an outlet 144G. The inlet 1441 is formed in the second surface 141 b of the first plate 141. The inlet 1441 opens to the discharge chamber 44. The inlet 1441 is located outward of the outlet 144G in the radial direction of the high-speed shaft 31. The outlet 144G opens to the first intermediate pressure passage 631. The outlet 144G is located outward of the sealing member 48 in the radial direction of the high-speed shaft 31. The bypass 144 is a passage that has the inlet 1441 connected to the discharge passage 62 and the outlet 144G connected to the space S between the back surface 41 a of the impeller 41 and the plate 14. The bypass 144 is a passage that has the inlet 1441 located outward of the outlet 144G and the outlet 144G located outward of the sealing member 48 in the radial direction of the high-speed shaft 31.

The bypass 144 includes a first bypass passage 145 and a second bypass passage 146. The first bypass passage 145 has the inlet 1441. The first bypass passage 145 extends from the inlet 1441 toward the second plate 142 through the first plate 141.

The second bypass passage 146 is formed by the accommodation recess 143 and the second plate 142. The second bypass passage 146 has the outlet 144G. The accommodation recess 143 has a bottom surface 143 a having a ring shape and an inclined surface 143 b. The bottom surface 143 a is a flat surface extending in the radial direction of the high-speed shaft 31. The inclined surface 143 b is a flat surface that has a ring shape and extends outwardly in the radial direction of the high-speed shaft 31 from the bottom surface 143 a toward the second surface 141 b. The inclined surface 143 b is inclined with respect to the axial direction of the high-speed shaft 31. A part of the inclined surface 143 b is communicated with the first bypass passage 145.

The second plate 142 has opposite surfaces, a first surface 142 a having a ring shape and a second surface 142 b having a ring shape, and an inclined surface 142 c. The first surface 142 a is in contact with the bottom surface 143 a of the accommodation recess 143.

The second surface 142 b is located on the opposite side of the first surface 142 a in the thickness direction of the second plate 142. The second surface 142 b is a flat surface extending in the radial direction of the high-speed shaft 31. The second surface 142 b is spaced from the back surface 41 a of the impeller 41 by a predetermined distance in the axial direction of the high-speed shaft 31. The inclined surface 142 c connects the first surface 142 a and the second surface 142 b. The inclined surface 142 c is a flat surface that has a ring shape and extends outwardly in the radial direction of the high-speed shaft 31 from the first surface 142 a to the second surface 142 b. The inclined surface 142 c is inclined with respect to the axial direction of the high-speed shaft 31.

The inclined surface 142 c of the second plate 142 is spaced from the inclined surface 143 b of the accommodation recess 143 by a predetermined distance. The inclination angle of the inclined surface 142 c with respect to the axial direction of the high-speed shaft 31 is equal to the inclination angle of the inclined surface 143 b with respect to the axial direction of the high-speed shaft 31. The inclined surface 142 c and the inclined surface 143 b cooperate to define the second bypass passage 146. The second bypass passage 146 has a ring shape to surround the high-speed shaft 31. The second bypass passage 146 extends, in the axial direction of the high-speed shaft 31, from a side on which the speed-up gear chamber 40 is located toward the impeller chamber 42, so as to become gradually distant from the high-speed shaft 31. The second bypass passage 146 serves as an outlet passage that extends to the outlet 144G outwardly in the radial direction of the high-speed shaft 31. The outlet 144G of the bypass 144 has a ring shape to surround the high-speed shaft 31.

The dimension of the thickness of the second plate 142 is greater than the dimension of the depth of the accommodation recess 143 in the axial direction of the high-speed shaft 31. That is, a part of the second plate 142 including the second surface 142 b projects from the accommodation recess 143 with the second plate 142 placed in the accommodation recess 143. The part of the second plate 142 projecting from the accommodation recess 143 is a projected portion 142 d that projects toward the back surface 41 a of the impeller 41. That is, the plate 14 includes the projected portion 142 d that projects toward the back surface 41 a of the impeller 41. The border between the inclined surface 142 c and the second surface 142 b projects from an edge of the inclined surface 143 b that is distant from the bottom surface 143 a in the axial direction of the high-speed shaft 31. Accordingly, the outlet 144G opens outwardly in the radial direction of the high-speed shaft 31. That is, the second bypass passage 146 opens outward of the projected portion 142 d in the radial direction of the high-speed shaft 31.

[Operation]

Next, the following will explain the operation according to the embodiment.

The pressure of the air discharged to the discharge chamber 44 is higher than the pressure of the air flowing through the intermediate pressure passage 63. Accordingly, the air having high pressure flows from the inlet 1441 to the outlet 144G through the bypass 144. The second bypass passage 146 extends to the outlet 144G outwardly in the radial direction of the high-speed shaft 31. As indicated by the arrow A in FIG. 3 , the air introduced from the inlet 1441 flows out of the outlet 144G through the second bypass passage 146 so as to form a flow of air flowing away from the sealing member 48 in the space S.

The rotation of the impeller 41 forms, on the back surface 41 a of the impeller 41, flow of air flowing outwardly in the radial direction of the impeller 41 by a centrifugal force of the impeller 41 as indicated by the arrow B in FIG. 3 . Accordingly, as indicated by the arrow C in FIG. 3 , the air flowing toward the sealing member 48 in the space S is likely to flow along the plate 14.

In this embodiment, the outlet 144G of the bypass 144 opens outward of the high-speed shaft 31 in the radial direction of the high-speed shaft 31. This configuration causes the air flowing toward the sealing member 48 along the plate 14 to collide with the air having high pressure discharged from the outlet 144G. The viscosity of the air having high pressure discharged through the projected portion 142 d and the outlet 144G draws the air in the second intermediate pressure passage 632 as indicated by the arrow D in FIG. 3 .

Accordingly, the air having high pressure discharged from the outlet 144G of the bypass 144 suppresses the flow of air toward the sealing member 48 in the space S. This suppresses leak of the air having high pressure from the impeller chamber 42 toward the speed-up gear chamber 40, thereby suppressing pressure increase in the speed-up gear chamber 40. Therefore, the vaporized or atomized oil is unlikely to be discharged outside the housing 11 through the pressure-relief passage 76 even if the impeller 41 keeps rotating at a high speed.

Advantageous Effect

Next, the following will explain the advantageous effects according to the embodiment.

(1) The bypass 144 suppresses the pressure increase in the speed-up gear chamber 40. This suppresses the discharge of the vaporized or atomized oil to the outside of the housing 11 through the pressure-relief passage 76 even if the impeller 41 keeps rotating at a high speed. This therefore suppresses the decrease in the amount of the oil filled in the centrifugal compressor 10.

(2) The outlet 144G of the bypass 144 has a ring shape to surround the high-speed shaft 31. This configuration allows the air having high pressure to be discharged from the outlet 144G to the whole circumference of the space S. This further suppresses the flow of air toward the sealing member 48 in the space S. Accordingly, this suppresses leak of the air having high pressure from the impeller chamber 42 toward the speed-up gear chamber 40, thereby suppressing the pressure increase in the speed-up gear chamber 40. This therefore further suppresses the decrease in the amount of the oil filled in the centrifugal compressor 10.

(3) The second plate 142 of the plate 14 includes the projected portion 142 d, and the second bypass passage 146 opens outward of the high-speed shaft 31 in the radial direction of the high-speed shaft 31. This configuration allows the air having high pressure discharged from the outlet 144G to flow in the opposite direction of the flow of air toward the sealing member 48 in the space S. This efficiently cancels the air flowing toward the sealing member 48 in the space S. This therefore suppresses leak of the air, which is flowing toward the sealing member 48 in the space S, to the speed-up gear chamber 40.

(4) The second bypass passage 146 extends, in the axial direction of the high-speed shaft 31, from a side on which the speed-up gear chamber 40 is located toward the impeller chamber 42, so as to become gradually distant from the high-speed shaft 31. This configuration improves the directivity of the air having high pressure discharged from the outlet 144G through the second bypass passage 146. This therefore enables the air having high pressure to be discharged from the outlet 144G so as to appropriately cancel the flow of air toward the sealing member 48 in the space S.

(5) In some cases, a part of the discharge passage 62 may protrude out of the housing 11 and have the inlet 1441 of the bypass 144. In such cases, a part of the bypass 144 may be formed of a pipe disposed outside the housing 11.

In this regard, according to the embodiment, the bypass 144 is formed in the housing 11. This configuration eliminates the need for additional member for forming the bypass 144. This therefore simplifies the configuration of the bypass 144.

<Modification>

The aforementioned embodiment may be modified as below. The embodiment may be combined with the following modifications within the technically consistent range.

-   -   In the embodiment, the bypass 144 is formed in the housing 11,         but the present disclosure is not limited thereto. For example,         a part of the bypass 144 may be formed of a member that is not a         member of the housing 11.     -   In this embodiment, the inclined surfaces 142 c and 143 b that         define the second bypass passage 146 may be a curved surface.         That is, the second bypass passage 146 only needs to extend, in         the axial direction of the high-speed shaft 31, from a side on         which the speed-up gear chamber 40 is located toward the         impeller chamber 42, so as to become gradually distant from the         high-speed shaft 31.     -   In this embodiment, the dimension of the thickness of the second         plate 142 may be equal to the dimension of the depth of the         accommodation recess 143 in the axial direction of the         high-speed shaft 31. In other words, the projected portion 142 d         of the plate 14 may be omitted. That is, the second bypass         passage 146 does not necessarily need to open outward of the         projected portion 142 d in the radial direction of the         high-speed shaft 31. In those modifications, the outlet 144G of         the bypass 144 opens in the axial direction of the high-speed         shaft 31.     -   In this embodiment, the outlet 144G of the bypass 144 does not         necessarily need to have a ring shape to surround the high-speed         shaft 31. For example, the outlet 144G may have a C-shape to         surround the high-speed shaft 31. In this modification, a part         of the inclined surface 142 c of the second plate 142 is in         contact with a part of the inclined surface 143 b of the         accommodation recess 143. However, the first bypass passage 145,         which is communicated with the inclined surface 143 b, is not         closed by the inclined surface 142 c.     -   In the embodiment, the plate 14 may not be formed of the first         plate 141 and the second plate 142. For example, the plate 14         may be formed of a single member. In this modification, the         second bypass passage 146 only needs to be formed in the plate         14 formed of a single member such that the second bypass passage         146 extends to the outlet 144G outward of the high-speed shaft         31 in the radial direction of the high-speed shaft 31. The plate         14 formed of a single member preferably has the projected         portion 142 d that projects toward the back surface 41 a of the         impeller 41. In this configuration, the second bypass passage         146 preferably opens outward of the projected portion 142 d in         the radial direction of the high-speed shaft 31. In this         modification, the projected portion 142 d of the plate 14 may be         omitted as well.     -   In this embodiment, the inlet 1441 of the bypass 144 may open to         the diffuser passage 43 or the discharge port 45. The bypass 144         only needs to to have the inlet 1441 connected to the discharge         passage 62.     -   In the embodiment, the first end of the pressure-relief passage         76 may be communicated with the speed-up gear chamber 40, and         the second end of the pressure-relief passage 76 may be opened         on the outer surface of the peripheral wall 13 b of the speed-up         gear housing 13 to be communicated with the outside. The         pressure-relief passage 76 may be modified as necessary as long         as the pressure-relief passage 76 may release the air in the         speed-up gear chamber 40 to the outside of the housing 11 as the         pressure in the speed-up gear chamber 40 increases.     -   In the embodiment, for example, the centrifugal compressor 10         may be mounted on a vehicle including an engine as a drive         source. For example, the centrifugal compressor 10 may not         include the electric motor 17. In this configuration, the         low-speed shaft 16 may be rotated by an engine mounted on the         vehicle.     -   In the embodiment, the centrifugal compressor 10 is not limited         to a centrifugal compressor that is mounted on a fuel cell         vehicle and supplies air to the fuel cell 47. For example, the         centrifugal compressor 10 may be used for an air conditioner to         compress refrigerant as a fluid. The centrifugal compressor 10         is not limited to a compressor mounted on a vehicle. 

What is claimed is:
 1. A centrifugal compressor comprising: a low-speed shaft that is rotated by a drive source; a high-speed shaft that is configured to rotate at a rotation speed that is higher than a rotation speed of the low-speed shaft; a speed-up gear that is configured to transmit power of the low-speed shaft to the high-speed shaft; an impeller mounted on the high-speed shaft; a housing having an impeller chamber for accommodating the impeller, a speed-up gear chamber for accommodating the speed-up gear and oil, a partition wall that separates the impeller chamber from the speed-up gear chamber and has an insertion hole through which the high-speed shaft is inserted, a pressure-relief passage for releasing air in the speed-up gear chamber to an outside of the housing, and a discharge passage to which the air compressed by rotation of the impeller is discharged; and a sealing member disposed between an outer peripheral surface of the high-speed shaft and an inner peripheral surface of the insertion hole, wherein the centrifugal compressor includes a bypass that is formed in the partition wall and has an inlet connected to the discharge passage and an outlet connected to a space between a back surface of the impeller and the partition wall, the inlet is located outward of the outlet and the outlet is located outward of the sealing member in a radial direction of the high-speed shaft, and the bypass includes an outlet passage that extends to the outlet outwardly in the radial direction of the high-speed shaft, and the air introduced from the inlet flows out of the outlet through the outlet passage so as to form a flow of air flowing away from the sealing member in the space.
 2. The centrifugal compressor according to claim 1, wherein the outlet of the bypass has a ring shape to surround the high-speed shaft.
 3. The centrifugal compressor according to claim 1, wherein the partition wall includes a projected portion that projects toward the back surface of the impeller, and the outlet passage opens outward of the projected portion in the radial direction of the high-speed shaft.
 4. The centrifugal compressor according to claim 1, wherein the outlet passage extends, in an axial direction of the high-speed shaft, from a side on which the speed-up gear chamber is located toward the impeller to chamber, so as to become gradually distant from the high-speed shaft.
 5. The centrifugal compressor according to claim 1, wherein the bypass is formed in the housing. 